In recent years, in response to increases in the level of integration and the performance of semiconductor large-scale integrated circuits (hereafter abbreviated as “LSI”), new fine processing techniques have been developed. One of these techniques is Chemical Mechanical Polishing (hereafter abbreviated as “CMP”). CMP is a technique that is used frequently in LSI production processes, and particularly in the planarization of insulating material portions in multilayer wiring formation steps, the formation of metal plugs, and the formation of embedded wiring and the like.
In recent years, the so-called damascene method has been used for forming embedded wiring. In the damascene method, a conductive substance portion is deposited on an insulating material portion having a surface in which recesses (such as grooves) and protrusions (such as bumps) have been formed in advance, thereby embedding the conductive substance within the recesses. Subsequently, the conductive substance deposited on the protrusions (namely, the conductive substance outside of the substance within the recesses) is removed by the CMP method to form embedded wiring.
In one example of CMP of a conductive substance portion, a polishing pad is first affixed to a circular polishing surface plate (platen), and the surface of the polishing pad is dipped in a CMP polishing liquid. The surface of the substrate on which the conductive substance portion has been formed is then pressed against the polishing pad, and a prescribed pressure (hereafter referred to as the “polishing pressure”) is applied from the back side of the substrate. Subsequently, with this state maintained, the polishing surface plate is rotated, thereby removing the conductive substance from the protrusions by the mechanical friction generated between the CMP polishing liquid and the conductive substance portion.
On the other hand, as illustrated in FIG. 4(a), usually, a barrier metal portion 2 is formed between the uneven insulating material portion 1 and the conductive substance portion 3 provided above that insulating material portion 1. The purposes of providing the barrier metal portion 2 include preventing diffusion of the conductive substance into the insulating material portion 1, and improving the adhesion between the insulating material portion 1 and the conductive substance portion 3. The barrier metal portion 2 is formed from a barrier-forming metal (hereafter also referred to as the “barrier metal”). Because the barrier metal is a conductor, the barrier metal needs to be removed in a similar manner to the conductive substance from those areas outside of the embedded recesses (namely, the wiring portions).
These removal processes are generally performed using a two-stage polishing method divided into a “first polishing step” of polishing the conductive substance portion 3 from the state illustrated in FIG. 4(a) until the state illustrated in FIG. 4(b), and a “second polishing step” of polishing the barrier metal portion 2 from the state illustrated in FIG. 4(b) until the state illustrated in FIG. 4(c), with a different CMP polishing liquid used for each of the polishing steps.
As design rules have become ever finer, the thickness of each of the above portions has also tended to decrease. However, as the barrier metal portion 2 becomes thinner, the effect of the barrier metal portion in preventing diffusion of the conductive substance tends to deteriorate. Further, the adhesion to the conductive substance portion 3 also tends to deteriorate. Moreover, as the width of the recesses (the width of the wiring) is narrowed, a new problem arises in that embedding the conductive substance within the recesses becomes more difficult (namely, the embeddability deteriorates), increasing the likelihood of holes known as voids occurring in the conductive substance portion 3.
For this reason, the use of cobalt (Co) as the barrier metal is being investigated. By using cobalt, diffusion of the conductive substance can be suppressed. Further, because cobalt also exhibits excellent affinity with the conductive substance (for example, copper-based metals such as copper and copper alloys), the embeddability of the conductive substance can be improved. Moreover, cobalt can also enhance the adhesion between the insulating material and the conductive substance.
When cobalt is used for the barrier metal portion 2, a CMP polishing liquid capable of removing cobalt must be used. A variety of compositions are known as CMP polishing liquids for metals, but such CMP polishing liquids are not necessarily capable of removing any metal. Among conventional CMP polishing liquids for metals, liquids for removing metals such as copper, tantalum, titanium, tungsten, and aluminum and the like are well known. However, although several liquids such as those disclosed in Patent Literatures 1-3 listed below have been reported as CMP polishing liquids capable of polishing cobalt, few such liquids are known.